Efficient cleaning of stencils
Using ultrasound against solder paste residues
After stencil printing, solder paste residue is deposited primarily in the corners and edges of the fine stencil openings and hardens there. This can lead to soldering errors in the subsequent reflow process, as the impurities change the amount of solder paste applied to the stencil. For this reason, the stencil must be thoroughly cleaned before it is used again.
Dried solder paste residues or SMD adhesive residues are particularly stubborn and cannot usually be removed by manual cleaning. However, ultrasonic cleaning ensures that even the finest apertures are thoroughly and gently cleaned of residues.
The Gensonic ultrasonic system from GEN3 was specially developed for cleaning steel and plastic stencils and reliably removes residues of solder paste and SMD adhesives.
How does ultrasonic cleaning work?
Ultrasonic systems clean the treated surface efficiently. The ultrasonic waves use alternating shock waves to create small bubbles in the applied cleaning fluid. These bubbles grow under the effect of the shock waves and implode as soon as they reach a certain size.
The implosion releases energy, some of which is converted into heat. High temperatures are generated in the bubbles, leading to an increase in pressure of up to 500 atm. The accumulated energy hits the surface at a speed of approx. 400 km/h and causes all impurities to detach from the surface.
In contrast to mechanical cleaning processes, ultrasonic technology enables the cleaning of the finest structures without deforming or damaging them.
The advantages of ultrasonic cleaning
- Gentle cleaning of the finest apertures
- improves the print quality on printed circuit boards
- reduces the cleaning effort on the printer
- Reduces the consumption of cleaning agents
- optimises the print-related error rate in electronics production
The cleaning process
The Gensonic ultrasonic cleaning device from GEN3, the SP6000 solder paste from Stannol and the Flux-Ex Pre cleaner from Stannol are used to demonstrate the cleaning process.
1.
The stencil to be cleaned is first clamped in the SCC stencil holder for the cleaning process. (Alternatively, cleaning can also be carried out directly on the printer - this eliminates the need to remove the stencil and set it up again).
2.
In the next step, a fresh fleece cloth is placed in the cleaning station below the stencil and coarse, superficial solder paste residues (here: Stannol SP6000) are removed with an IPA cleaning cloth (here: Stannol citrus cleaning cloth).
3.
Next, spray the stencil generously with a suitable cleaning agent (here: Stannol Flux-Ex Pre). Attention: It is important that a closed liquid film is created on the surface to be cleaned: There must always be a thin film of cleaning agent between the ultrasonic transducer and the stencil.
4.
The oscillating head of the ultrasonic cleaning device (here: Gensonic from GEN3 Systems) is now activated using the foot switch. The oscillating head is moved evenly over the surface to be cleaned until all impurities have been removed. The cleaning process is completed within a few minutes.
5.
The solder paste residue is absorbed by the fleece cloth underneath the stencil. The fleece can simply be removed and disposed of after cleaning.
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